Fine powders capable of imparting conductivity to plastics and paints to which the powder is added are known, such as tin oxide type powders, zinc oxide type powders; powders of titanium oxide, aluminum oxide or the like coated with tin oxide; and fibrous materials such as potassium titanate fiber, gypsum fibers and glass fibers coated with electrically conductive tin oxide.
As is well known, to impart good electrical conductivity to plastics and paints, it is necessary to incorporate a large amount of powder thereinto so that every adjacent particle comes into contact with one another, thereby rendering the use of the conductive powder very expensive, and only fit for limited purposes.
To eliminate such a disadvantage, the use of the aforesaid needle-like powder has been proposed which has an extremely larger aspect ratio than that of spherical powder, which makes it possible to increase contact probability of added electric conductivity-imparting filler, even when used in a smaller amount.
However, all of such needle-like powders are obtained by coating a core material with an electrically conductive material. Although such a powder makes it possible to reduce the amount thereof to be used, the coated layer suffers from peeling off from the core material when it is added to plastics and paints for imparting electrical conductivity thereto and thus a desired conductivity-imparting effect can hardly be attained.
On the other hand, a variety of methods for preparing electrically conductive zinc oxides are disclosed, for instance, in Japanese Patent Laid-Open Application corresponding to OLS in Germany (hereinafter referred to as "J. P. KOHKAI") Nos. Sho 58-161923, Sho 58-145620, Sho 55-162477 and Sho 59-97531, Japanese Patent Publication corresponding to Auslege in Germany (hereinafter referred to as "J. P. KOHKOKU") No. Sho 55-19897 and U.S. Pat. No. 3,538,022. All of these methods however, relate to formation of spherical or particulate powder, but not the formation of needle-like conductive zinc oxide. Regarding methods for preparing needle-like zinc oxide, there are methods known according to a gas phase reaction such as disclosed, for instance, in "Handbook of Crystallographic Engineering", p. 720, issued by KYORITSU PUBLISHING CO., LTD., or those disclosed in "Bulletin of the Society of the Ceramic Industry", 1984, 92(4), p. 227. However, none of such methods relates to the production of electrically conductive zinc oxides.
In view of that set forth above, it is thus an object of the present invention to provide electrically conductive zinc oxide powder effective for greatly decreasing specific volume resistance of a base material such as a resin even if the powder is added to the base material in a relatively small amount compared to amounts of conventional materials required to produce the same effect, and which also has excellent whiteness.
It is a further object of the invention to provide a conductive powder which, when incorporated into a base material, does not lose its conductivity during mixing.
Additional objects of this invention will become apparent from the following description.